Discuss some basic knowledge of interface method parameters in JavaScript

When writing JavaScript code, it is often necessary to call interface methods to implement certain functions. Interface methods refer to a set of commonly used functions that define some regular operations and can be called by other functions or modules. When calling interface methods, we also need to pass some parameters to them, which are used to control the behavior of the interface method. This article will discuss some basic knowledge of interface method parameters in JavaScript.

1. Definition of method parameters

When defining an interface method, a pair of parentheses is usually added after the function name. The parameter list required by the method can be specified within the parentheses. For example, the following code defines a method named showMessage, which requires two parameters, text and color:

function showMessage(text, color){
//Method body
}

When calling the showMessage method, we need to pass two parameters to it:

showMessage("Hello World!", "red");

In this way, the showMessage method The text Hello World! will be displayed in the document in red.

2. Passing function parameters

In JavaScript, there are two ways to pass parameters, namely passing by value and passing by reference.

1. Value passing

Value passing refers to copying the value of the parameter and passing it to the function. Within the function, modifying the value of the parameter will not affect the value of the original parameter. For example:

function changeValue(num){
num = 5;
}
var x = 10;
changeValue(x);
//At this time x is still Equal to 10

In the above code, the changeValue method receives a parameter num, whose initial value is 10. When the changeValue method is called, a copy of the value of x will be passed to the num parameter. Inside the changeValue method, change the value of num to 5. However, this modification does not affect the value of the x variable, x is still equal to 10.

2. Passing by reference

Passing by reference refers to passing the reference of the parameter to the function. Within a function, modifying a parameter's attribute or element affects the original parameter's value. For example:

function changeArray(arr){
arr[0] = 5;
}
var myArray = [1, 2, 3];
changeArray(myArray);
//At this time, the value of myArray is [5, 2, 3]

In the above code, the changeArray method receives a parameter arr, which is an array. When the changeArray method is called, a reference to myArray is passed to the arr parameter. Inside the changeArray method, modify the first element of the arr array to 5. Since myArray and arr refer to the same array, this modification will also affect the value of myArray.

3. Default values ​​of parameters

JavaScript also provides a convenient function, which is to set default values ​​for function parameters. When a function is called, if a parameter is not passed, the parameter will have a default value. For example:

function showMessage(text, color="black"){
//Method body
}

In the above code, the second parameter of the showMessage method color sets a default value of black. If the color parameter is not passed in when calling, the parameter will use the default value. For example:

showMessage("Hello World!");
//The color will default to black at this time

If you need to pass other values ​​to the color parameter, you only need to pass in the corresponding The parameters are:

showMessage("Hello World!", "red");
//The display color is red at this time

4. Indefinite parameters

In some cases, we may need to define a function that accepts a variable number of parameters. In JavaScript, you can use rest parameters to implement functions with variable parameters. For example:

function sum(a, b, ...nums){
var result = a b;
for(var i=0; i

  result += nums[i];

}
return result;
}
sum(1, 2, 3, 4, 5);
//The result at this time is 15

above In the code, the sum method receives two parameters a and b, as well as a set of variable number of parameters nums. Inside the method, after adding a and b, use a loop to accumulate the elements in the nums array to get the final result.

5. Summary

In JavaScript programming, interface method parameters are essential. There are two ways of passing parameters: passing by value and passing by reference. For ease of use, you can set default values ​​for function parameters. In addition, when the number of function parameters is variable, rest parameters can be used to implement functions with variable parameters. Mastering the basic concepts and usage of these method parameters will help you better use JavaScript for development.

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